I bought an Auto Gear M-23Z off a board member that decided to go TKX. An M-23Z is a Muncie clone with everything better than Muncie designed. It is an utra-wide ratio transmission with a 2.98:1 first gear and an even drop between each gear with a 1:1 4th gear. I have had it for almost 3 years now and I finally, FINALLY got to install it in my GS 350 with the freshly rebuilt 350. To say I was excited would be an understatement. It looks like a beefy Muncie if no cost were spared. It bolts to the bellhousing, the same clutch splines and and the shifter bolted up like factory, complete with back drive for the reverse to lock the column. The only issues I had were minor. First, I had the drive shaft shortened, a new yoke put on because even the Muncie felt like at full droop, it was too tight. Second, the back drive stud had to be reworked due to the change in thread size on the two transmissions. So, after finally getting everything together, we took it for the first test drive. Now, if you have 3.08 rear gears and an M21, you know it feels like taking off in second gear. It feels painful to me. When compared to the M-21 2.20:1 first gear, the 2.98:1 M-23Z first gear makes the 3.08:1 rear gears take off like it has 4.11:1 rear gears. My wife can drive it and didn't kill it. Compared to the M-21 and the M-20 I'd had in it before, it was very firm in shifts. It takes a little more effort to get the shifter to move into gear but not excessive. It also whines a bit in the lower gears like an M-22 would but it largely goes away in 4th gear. Overall, if you have a Muncie but want something different, the M-23Z is a pretty sweet option that most people wouldn't notice if they looked under it.
I've got one that I need to finish putting together. Also got the heavier AutoGear case. Still need to get a Hurst shifter for it. Going to run a hydraulic clutch, though. Running a 455 with a 3.08 rear. I bought all my parts through Paul Cangialosi( https://www.5speeds.com/cart/index.php?route=common/home ) He calls it an M22z. Nice setup! I know I'm looking forward to when I finally get mine done!
His website is pretty bare at the moment. I originally looked for the ultrawide gear set for my numbers match M-21. Those gear sets are out of stock everywhere. I didn't build it or order it but it seemed like a great swap for a Muncie M-21. It feels pretty good now. About the only thing I'd do is to change to 2.73:1 rear gears. That would make it like 3.73:1 gears and still cruise at 2.73:1 speeds. Even with 3.08:1 gears, it cruises at 75MPH at 3,000 RPM. It feels pretty good going down the road at that speed/RPM. I can swap to 275/60-15 on the rear to get it down to 2,800 RPM at 75MPH.
There were a few parts that I was needing that showed as out of stock on his website, but he was able to find what I needed. He gets parts in all the time, and he supposedly goes through and checks and deburrs all of them before he puts them up on his website for sale. So, even if it's listed as out of stock, he may have some that he wasn't quite ready to list yet, but will prep and send out if he has it. I called and talked to him, and mentioned I was wanting to place an order, but wanted to order everything, but everytime I checked his site, he was always out of something different. The time I called was when he had almost everything I needed at that time, but was only missing a few items. Told him what else I needed and he was able to come up with them. He doesn't even have the 22z parts listed anymore. If you download the parts diagram/catalog, it's still in there, but nothing on his shopping page. Must be supply chain problems. Those gearsets are made in Italy, I believe. I'm sure I'll find a part or two that I'm missing that I'll need to call him about, I just need to start assembling what I've got. Real good guy to talk to and he takes the time to answer any questions you have. Also, he has a YouTube channel, GearboxVideo that he has real good disassembly and assembly videos on all kinds of manual transmission stuff.
I have a factory Hurst shifter with rods minus the handle. Don't need the shifter since I bought a 5 speed
I've got a little over 100 miles on this M-23Z AutoGear transmission and I'm loving it. It takes off much better than the M-21 with its 2.20 first gear. That is nearly as high as second gear in the M-23Z. Now, if I skip a gear, it is because I was winding it up in a lower gear and glanced a cop car.
A little over a month and a few 100 miles later I've still not been too hard on it since the clutch is supposed to get 500 miles of easy driving. I'm still loving the low first gear. I put my 275-60-15 tires on the back and it still didn't lug it down at all. It is still a very firm transmission. Up shifts are solid and no mistaking if it is in gear or not. Down shifts take a little effort or need some rev matching if I'm trying to bleed speed by engine braking in the next lower gear. I suspect that will get better with more miles. All in all, I like the whine in 1st, 2nd and 3rd gear. Very good alternative to the fab work needed to get a 5 or 6 speed.
